1. Field
The present disclosure relates to a die structure, a manufacturing method and a substrate thereof.
2. Related Art
In recent years, LEDs having such advantages as power saving, environmental friendly, quick response and controllable light emission spectrum have gradually replaced the conventional light sources. The performance of LED has been continuously improved to satisfy the requirement for general lighting; however, in high power LEDs (e.g. greater than 1 W), the heat dissipation becomes critical issue due to its rapidly generating of heat during operation. The main reasons lie in that, only 15% to 20% of electrical energy can be converted into the light energy, and the rest of energy will be consumed and dissipated in heat form. Thus, if the heat cannot be dissipated to atmosphere in time, temperature of the LED chip (or die) disposed on the substrate will rise up to extremely high and consequently the conversion efficiency and life time of LED will be rapidly decreased.
At present, one of the approaches to improve heat dissipation capability of LED package has been focused on the material of the substrate. For example, metal core printed circuit board (MCPCB) is formed by hot-pressing of an aluminum alloy heat dissipation layer, an insulating adhesive layer and a metal circuit layer (copper foil). Due to its high thermal conductivity of aluminum alloy, the heat dissipation can be enhanced. Although the thermal conductivity of the MCPCB may achieve 1 W/mK to 2.2 W/mK, which can satisfy the requirement of a part of high power LEDs, the heat dissipation capability have been limited by thermal conductivity of the insulating adhesive. Moreover, since the coefficient of thermal expansion (CTE) of the MCPCB and that of the LED chip (or die) are mismatched, the LED chip is easily influenced by the temperature changes; as a result, the reliability and life time of LED package will be rapidly reduced because of peeling, cracking or failing on LED chip.
Compared with the metals, the ceramic materials have the CTE relatively closed to that of the LED chip; therefore, in current development of the high power LED, ceramics are commonly used to be the substrate material. In general, ceramic raw materials include clay minerals, such as aluminum oxide, aluminum nitride, silicon carbide, tungsten carbide, and other oxide, non-oxide and composite materials, and its shape can be formed by casting, molding, pressing, or other approaches. In LED applications, conductive pillars are required in ceramic substrate for heat dissipation and power transmission. By filling conductive slurry after mechanical drilling on solidified ceramic substrate, or by stacking and solidifying a plurality of ceramic raw material layers with horizontal-aligned slurry-filled through hole, conductive pillar can be obtained in the substrate as the heat and electricity pathway to improve electrical and thermal conductivity of ceramic substrate.
In conventional ceramic substrate, to enable the ceramic substrate to have a lower CTE and a higher electrical or thermal conductivity, the method includes disposing a plurality of through holes on the ceramic substrate by mechanical or laser drilling process and filling metal slurry into the through holes to form electrical or thermal pathway in the ceramic substrate. However, this method of disposing the electrical or thermal pathway requires machine tools to serially drill the substrate, and the minimum pitch of through holes is limited by the process and tools (typically 0.4 mm). The mechanical drilling consumes longer manufacturing time to form vias on higher density of through holes or on higher hardness ceramics.
In addition, to let the metal slurry smoothly filled into the holes without void defects, the diameter of through hole should be large enough; consequently, the contact area between LED chip and the filled holes, as well as through hole density will be limited in previous approaches. Due that the pathway cannot be distributed in a high density (larger than 0.4 mm-pitch), LED die or chip needs to be aligned before bonding to the substrate to ensure the LED die or chip locating at proper position and contacting with the pathway. Besides increasing the complexity of fabrication process, the throughput of total LED packaging is decreased.